code: def __init__(self, session_id: str):
      self._session_id = session_id
      self._slots_ref = None
  
      self._cluster_api = None
      self._meta_api = None
  
      self._bands = []
      self._address_to_bands = dict()
      self._device_type_to_bands = dict()
      self._band_watch_task = None
  
file_path: mars/mars/services/scheduling/supervisor/assigner.py
imports: import asyncio
  import itertools
  import numpy
  from collections import defaultdict
  from typing import Dict, List, Set
  from ....None import oscar
  from ....core.operand import Fetch, FetchShuffle
  from ....typing import BandType
  from ...core import NodeRole
  from ...subtask import Subtask
  from ..errors import NoMatchingSlots, NoAvailableBand
label_desc: Use image node_id 2 to create a new AssignerActor object from inherited base classes: mo with example: obj = AssignerActor(session_id)